Not sure what the average age is, but my daughter is 12. She just had two removed by the dentist as she is due to have a brace next spring and they want to catch the two adult teeth as they come through as they are due to grow inwards (her other teeth stick outwards severely the other way). She has one left which is a little wobbly, so for her I'd say she will have all her adult teeth before she is 14.